chore(Popover): Remove the CSS modules feature flag for the Popover component

[jonrohan]

Closes https://github.com/github/primer/issues/4505
Closes https://github.com/github/primer/issues/4139

Changelog

New

Changed

Removed

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 03f25b6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	96.57 KB (-0.53% 🔽)
packages/react/dist/browser.umd.js	96.83 KB (-0.49% 🔽)

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/376662

[primer-integration]

🟢 golden-jobs completed with status success.

[Copilot]

Pull Request Overview

This PR removes the legacy CSS modules feature flag from the Popover component and standardizes on the new toggleSxComponent approach for both Popover and Popover.Content.

• Drop styled-components and useFeatureFlag–based toggling logic
• Introduce toggleSxComponent for Popover wrapper and content
• Update the changeset to reflect a minor version bump

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/react/src/Popover/Popover.tsx	Removed CSS modules flag and styled-components code; added toggleSxComponent usage
.changeset/green-carpets-float.md	Added changeset entry for the minor bump removing the CSS modules flag

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!